Writing help

How to write a good plot twist

1. Give it an open ending.
Not necessarily the easiest, but one of the most practical plot twists is the ambiguous ending. It is a good one to use if you don't want your overall storytelling to be affected by your plot twist too much.
When you leave a story open ended, this means you don't explain how the story ends, but rather, you leave it up to the imagination of the reader.
The audience doesn't know what happened to the characters in the end, but based on the story and what has occurred thus far, they can wager a guess and infer an ending in order to satisfy their need to tie up the loose ends in their minds.

2. Use an untrustworthy narrator.
This is a great technique to use because people are often conditioned to take the narrator's word when reading a story. The narrator is the perfect character to use in order to confuse the reader, and maybe give them hints and suggestions that will lead them to a completely different conclusion from the one that you are setting up for your plot twist.
If you are going to use this method, however, it's important to not make it glaringly obvious that the narrator is untrustworthy in telling the story. You should be foreshadowing it subtly, but the story that the narrator is telling must also be completely believable.
When used effectively, the reader will be very surprised at the plot twist, but will also have a feeling of "I should have seen it coming," as well.

3. Reverse character roles.
A pretty straightforward approach, this is when your plot twist consists of either the hero turning into the villain or vice versa.
Sometimes it comes off forced when the character becomes a polar opposite of what he or she has been throughout the story, so it is best to give these characters some traits that would make their transitions believable.

4. Throw your reader into the mix.
A good way to make plot twists work well is by starting the storytelling in the middle of some type of climax. When you do this, you are giving the reader an immediately intriguing plot that could really go anywhere, because there is no backstory to reference.
The lack of prior information about the situation given to the reader gives the writer a lot of freedom with the plot twists that he or she plans.

5. Try an unexpected kill.
Your readers might hate you for a short while, but this technique provides an unexpected plot twist.
Killing off one of the main characters in the middle of the story is something that always comes as unexpected. Readers pick up on who the key characters are early in the story if they are well-developed, and they attach to these characters early on in the story.
Having one of these main characters die really twists things into an unexpected direction, because the reader is already looking forward to what will happen to this character at the end of the story. Finding out that this character will not be playing any type of role in the story's ending is always a good shock for the reader.
These are only a few suggestions. There are many other great ways to introduce plot twists into your stories, which can help you to take your writing into a completely new direction.

1. Eliminate the obvious
When coming up with the climax to your story, discard every possible solution you can think of for your protagonist to succeed.
Then think of some more.
And discard those, too.
You're trying to create an ending that's so unforeseen that if a million people read your book, not one of them would guess how it ends (or how it will get to the end), but when they finally come to it, every one of those people would think,Yes! That makes perfect sense! Why didn't I see that coming?
The more impossible the climax is for your protagonist to overcome, the more believable and inevitable the escape or solution needs to be. No reader should anticipate it, but everyone should nod and smile when it happens. No one guesses, everyone nods. That's what you're shooting for.
While writing, ask yourself: 
What do I need to change to create a more believable world for each separate twist I'm including?
How can I drop the gimmicks and depend more on the strength of the narrative to build my twist?
Will readers have to "put up with" the story that's being told in anticipation of a twist ending, or will they enjoy it even more because of the twist? How can I improve the pretwist story?
How can I make better use of the clues that prove the logic of the surface story to create the twist and bring more continuity to the story—but only after the twist is revealed?